Seyne-Les-Alpes: Dozens of specialised police and rescue workers kicked off a fourth day of recovery operations on Friday at the scene of the crashed Germanwings jet, hunting for its second black box.

Officials are also combing the wreckage for body parts and DNA samples that would enable them to identify the 150 people that died in the crash, apparently deliberately initiated by co-pilot Andreas Lubitz.

"There's not much plane debris left. There's mainly a lot of body parts to pick up. The operation could last another two weeks," said police spokesman Xavier Vialenc.

There are 15 specialists on site, 10 to take DNA samples and five detectives running the legal investigation.

Nearby, around 40 technicians are working on the DNA samples from the crash site, comparing them to samples taken from the families.

A local building has been commandeered and turned into a biological analysis unit, with several white tents running off generators.

The vast majority of the bereaved family members have now left the remote site in the French Alps where the Germanwings Airbus A320 smashed into the mountain.

French prosecutors said yesterday that Lubitz "deliberately" initiated the descent and seemed to "want to destroy" the plane in an act that German Chancellor Angela Merkel described as "unimaginable."

Germany and Spain bore the brunt of the tragedy, with 75 Germans dead and at least 50 Spanish on board the Barcelona to Duesseldorf flight.

French Prime Minister Manuel Valls said that "everything is pointing towards an act that we can't describe: criminal, crazy, suicidal."

"It's up to the legal investigators -- especially the Germans and of course Lufthansa -- to shed light on the career and profile of this pilot," said Valls.

French prosecutors have been able to listen to the voice recordings made in the cockpit before the crash but are still searching for the second black box that contains technical flight data.